In the dispensing of substances such as, for example, cleaning or other compounds, it is common to use a water driven venturi to create a vacuum to suck up a selected chemical substance into the water stream where it is diluted for downstream dispensing. Where it is desired to dispense more than one mixture, a select valve is used to select which of several chemicals will be sucked into the water stream.
One such select valve is described in U.S. Pat. No. 5,377,817 which is expressly incorporated herein by reference as if fully reproduced herein.
Reference is also made to applicant's corresponding application Ser. No. 08/673,332 filed Jun. 28, 1996 which in part discloses an improvement to U.S. Pat. No. 5,377,718 and which is also expressly incorporated herein by reference.
In these two disclosures, a rotatable sealing disc has a sealing face urged against the opposed sealing face of a multiple port plate. The sealing disc has at least one blind slot extending radially outwardly from a center outlet or venturi port. The sealing disc can be rotated to move the blind slot about the center port so the other end of the slot overlies a selected inlet port connected to at least one source of a chemical to be sucked into the venturi for dilution and dispensing. Rotation of the sealing disc thus selects an inlet port to be connected to the common center outlet or venturi part so a selected chemical can be dispensed.
Once a selected chemical is dispensed, the chemical flows from the chemical conduit or pick up line through the inlet port into the blind slot and through the outlet port through a passage to the venturi. When another chemical is selected, it is typical to stop the water flow and then turn the sealing disc to align the blind slot with the new inlet port. It will be appreciated, however, that portions of the first selected chemical remain in the blind slot, center port and passage to the venturi. Thus, when the second chemical is dispensed, the first effluent is compromised or contaminated by remnants of the first selected chemical. This initial contamination may not last long, but where mix ratios are critical, or purity of the dispensed effluent is desired, this contamination constitutes a problem.
One method of cleaning the common passages of a select valve, prior to dispensing a newly selected chemical, is to purge the passages by selecting an inlet port connected to a purge compound. This requires selection of a purge position, and venturi operation for the duration of the purge. This thus requires operation of the final dispenser into a purge recirculation or waste tank and obviously requires extra time and the expense of apparatus associated with the purge operation.
It has thus been one objective of the invention to provide apparatus for purging common passages in a select valve prior to selection of a second compound to be dispensed.
A further objective has been to provide apparatus for removing a first selected chemical from the common passages of a select valve prior to selection of a second chemical.
A further objective has been to provide apparatus for purging passages of a valve without flushing with a purge material.
A further objective has been to provide improved methods for purging a select valve.